Magnetic recording medium and hard disk drive using the same, and manufacturing method thereof

ABSTRACT

A magnetic recording medium, a hard disk using the same, and a manufacturing method thereof are provided. In one example, the magnetic nano-particle medium is formed by depositing a magnetic nano-particle colloid on a substrate, wherein the axes of easy magnetization of respective crystalline particles are aligned with high accuracy. A layer of L10 alloy nano-particles which will exhibit magnetic properties through an order-disorder transition, and arranged at a substantially uniform spacing on a substrate, and a carbon-containing covering film for surrounding these nano-particles and making the spacing substantially uniform are provided. To the L10 alloy of the nano-particles, at least one non-magnetic element is added, or a covered layer comprising at least one non-magnetic layer is formed therearound. This makes it possible to implement a magnetic recording medium wherein the average diameter of nano-particles is small, and the nano-particle diameter dispersion is small, and the axes of magnetic anisotropy are aligned.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. application Ser. No. 10/456,619filed Jun. 9, 2003. This application claims priority to U.S. applicationSer. No. 10/456,619 filed Jun. 9, 2003, which claims priority toJapanese Patent Application No. 2002-270895 filed Sep. 18, 2002, thecontents of which are hereby incorporated by reference into thisapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to recording mediums and, moreparticularly, to a magnetic recording medium, a manufacturing methodthereof and a hard disk drive equipped with the same.

2. Discussion of Background

The real recording density of a hard disk drive has been steadilyincreasing, and is expected to reach 100 Gb/in.² by 2003. However, ifthe bit length to be recorded decreases due to a further increase indensity, the diameter of crystalline particles constituting a recordingmedium is required to be further decreased in order to keep the signalto noise ratio of the signal recorded on the medium. The reduction indiameter of the crystalline particles, however, increases the thermalinstability of magnetization of the medium. Unfavorably, this, in turn,causes the recorded signals to vanish.

In particular, when the particle diameter dispersion of the crystallineparticles is large, unfavorably, the recorded magnetization signal ofthe crystalline particles with a smaller particle diameter vanishes evenif the crystalline particles of an average particle diameter areresistant to thermal instability. Namely, to meet the further increasein density, it is essential to develop a magnetic recording medium madeup of crystalline particles with a smaller average diameter and asmaller particle diameter dispersion.

As a technology for solving the problem, for example, the followingmethod as described in Appl. Phys. Lett., Vol. 75, No. 20, pp. 3162-3164(1999) is proposed as a first method using a conventional sputteringprocess: FePt particles having a high anisotropy constant are sputteredsimultaneously with SiO₂ to form a granular film of FePt and SiO₂, sothat a FePt medium with a particle diameter of not more than 10 nm isformed.

Whereas, in Journal of the Magnetics Society of Japan, Vol. 25, pp.847-850, (2001), there is disclosed a second method: FePt nano-particlesare deposited very thinly to a thickness of not more than 4 nm on a MgOunderlayer. This induces the island growth of the FePt nano-particles,so that FePt nano-particles with a particle diameter of not more than 10nm are formed. Further, in Abstracts of the 25th Annual Conference ofthe Magnetics Society of Japan, p. 23, (2001), there is describedanother method obtained by improving this method, in which the filmthickness is increased by multilayer film growth.

These methods are the methods for manufacturing a medium by a sputteringprocess conventionally used in manufacturing of a medium. In Science,Vol. 287, pp. 1989-1992, (2000), there is disclosed a third method: aFePt nano-particle colloid is chemically synthesized, and expanded andself-assembled on a substrate to form a magnetic recording medium inwhich the average diameter of nano-particles and the nano-particlediameter dispersion are 5 nm and not more than 10%, respectively, bothof which have been largely reduced from those of the existing magneticrecording media. Further, a detailed description on the third method isfound in JP-A Nos.48340/2000 and 54012/2000.

However, the proposed methods in the prior art present the followingproblems. With the first method using a granular film, it is possible tomanufacture crystalline particles with smaller particle diameter.However, it is difficult to reduce the dispersion of particle diameters.Further, in order to make the crystalline particles commerciallyavailable as a medium, the axes of magnetic anisotropy of the respectivecrystalline particles are required to be aligned in a certain directionwith high accuracy. However, this is difficult to achieve with thismethod. In a recent year, in Appl. Phys. Lett., Vol. 77, No. 14, pp.2225-2227 (2000), there has been disclosed a method in which the axes ofeasy magnetization of FePt are aligned perpendicular to the substrateplane using B₂O₃ in place of SiO₂. However, a method for reducing theparticle diameter dispersion is not disclosed therein.

With the second method, FePt nano-particles are deposited very thinly onan underlayer through island growth by a sputtering process, and thegrown nano-particles are stacked in multilayered structure to form amedium. It is reported that the nano-particle diameter of the medium isincreased by the heat treatment for inducing the magnetization of theFePt nano-particles with the second method.

With the third method in which a chemically synthesized FePtnano-particle colloid is self-assembled on a substrate to manufacture amedium, it is possible to achieve the reductions in average diameter ofnano-particles and nano-particle diameter dispersion. However, the axesof magnetic anisotropy of the respective crystalline nano-particles areoriented at random.

SUMMARY OF THE INVENTION

It is an object of the present invention to reduce the average diameterof nano-particles and the nano-particle diameter dispersion.

It is another object of the present invention to develop a method foraligning the axes of magnetic anisotropy of the nano-particles with highaccuracy.

In accordance with the present invention, it is possible to implement anano-particle medium with a high magnetic anisotropy energy wherein theaverage diameter of nano-particles and the nano-particle diameterdispersion are very small, and the axes of easy magnetization of thenano-particles are aligned. Therefore, it is possible to implement ahard disk drive using the same medium, which is thermally stable, andexhibits a high resolution and a super-high recording density.

In the present invention, a magnetic recording medium in which theaverage diameter of nano-particles and the nano-particle diameterdispersion have been both largely reduced from those of the existingmagnetic recording media is formed by employing the foregoing thirdmethod. Namely, an alloy nano-particle colloid is chemically synthesizedso that alloy nano-particles with an average nano-particle diameter ofnot less than 1 nm and not more than 20 nm, and a nano-particle diameterdispersion of not more than 10% are surrounded by an organic compound,and arranged at a substantially uniform spacing. The resulting alloynano-particle colloid is caused to undergo a so-called self-assemblingon a substrate to form a magnetic recording film.

The alloy nano-particles immediately after chemical synthesis arenon-magnetic. For example, in the case of FePt nano-particles, thenano-particles are required to undergo an order-disorder transition incrystal structure by a high temperature heat treatment at not less than550° C., and thereby to exhibit magnetic properties. However, at such ahigh ordering temperature, the organic compound surrounding thenano-particles is solidified before the nano-particles exhibit magneticproperties. As a result, the nano-particles are fixed with their axes ofeasy magnetization oriented in random directions. Therefore, it isdifficult to align the axes of easy magnetization uniformly in a desireddirection even if a prescribed magnetic field is externally appliedthereto. Whereas, for a perpendicular magnetic recording medium in whicha magnetic recording film is formed on a substrate with a soft magneticunderlayer interposed therebetween, if a high temperature heat treatmentis performed for causing a desired magnetization of the magneticrecording film, the magnetic characteristics of the soft magneticunderlayer is adversely affected. As a result, it becomes impossible toexpect the effects of the provision of the soft magnetic underlayer tobe produced. Therefore, it is difficult to form a magnetic recordingfilm having desirable magnetic characteristics. Thus, it is difficult toobtain a perpendicular magnetic recording medium adaptable to highrecording density in which the average diameter of nano-particles issmall, and the nano-particle diameter dispersion is small, and further,the axes of magnetic anisotropy are aligned.

In the present invention, the ordering temperature at which the alloynano-particles undergo an order-disorder transition to exhibit magneticproperties is made lower than the stiffness temperature of the organiccompound surrounding the nano-particles. Thus, the nano-particles areapplied with a prescribed magnetic field while exhibiting magneticproperties through the order-disorder transition. As a result, theorganic compound is solidified with the axes of easy magnetization ofthe alloy nano-particles aligned substantially uniformly along aspecific direction.

In accordance with the present invention, it is possible to obtain amagnetic- recording medium, which comprises: a substrate; and a magneticrecording layer formed on the substrate, the magnetic recording layercomprising an organic compound and alloy nano-particles surrounded bythe organic compound and arranged at a substantially uniform spacing,the alloy nano-particles undergoing a transition into an orderedstructure at a lower temperature than the stiffness temperature of theorganic compound to exhibit magnetic properties, wherein the organiccompound has been solidified with the axes of easy magnetization of thealloy nano-particles aligned substantially uniformly along a specificdirection with respect to the substrate plane.

In the present invention, there is provided a magnetic recording medium,which comprises: a substrate; a layer of L10 alloy nano-particlesarranged at a substantially uniform spacing on the substrate, andexhibiting magnetic properties through an order-disorder transition; anda carbon-containing covering film surrounding the nano-particles formaking the spacing between the nano-particles substantially uniform. Tothe L10 alloy of the magnetic nano-particles, at least one non-magneticelement has been added. Alternatively, a covered layer comprising atleast one non-magnetic element has been formed therearound. Thisimplements a magnetic recording medium using a magnetic recording layercomprising alloy nano-particles with a small average diameter ofnano-particles and a small nano-particle diameter dispersion, andfurther with the axes of magnetic anisotropy aligned uniformly along adesirable direction. In particular, the temperature causing the magneticL10 alloy nano-particles to undergo an order-disorder transition andthereby to exhibit magnetic properties is made lower than the stiffnesstemperature of the organic compound surrounding the alloynano-particles, for example, the temperature is lowered to not more than300° C. This implements the uniform alignment of the axes of magneticanisotropy of the nano-particles.

Further, each of the L10 alloy nano-particles is composed of a materialcomprising an alloy of any of Fe and Co and any of Pt and Pd as a base,and any of Cu, Sn, Pb, Sb, and Bi added thereto. Still further, thecontent of Cu, Sn, Pb, Sb, or Bi to be added of the L10 alloynano-particles is set in a range of 5 to 20%. Alternatively, each of theL10 alloy nano-particles is so configured that an alloy of any of Fe andCo and any of Pt and Pd is included as a core, and any element of Cu,Sn, Pb, Sb, Bi, and Ag surrounds therearound.

Further, the axes of easy magnetization of the alloy nano-particles areset along any predetermined, specific direction of the directions atangles of roughly 0 degrees, roughly 45 degrees, and roughly 90 degreeswith respect to the substrate plane. In particular, the magneticrecording medium is composed of a nano-particle layer wherein the axesof easy magnetization of the nano-particles are at an angle of roughly45 degrees or roughly 90 degrees with respect to the substrate plane, asubstrate, and a soft magnetic underlayer.

Further, a hard disk drive is comprised of a magnetic recording mediumwherein the axes of easy magnetization are aligned at an angle ofroughly 0 degrees with respect to the substrate plane; and amerged-type-magnetic head composed of a reader using a magneto-resistiveeffect and a writer in a ring form. Alternatively, a hard disk drive iscomprised of a magnetic recording medium so configured that anano-particle layer, wherein the axes of easy magnetization are alignedat an angle of roughly 45 degrees or roughly 90 degrees with respect tothe substrate plane, is formed on a substrate with a soft magnetic layerinterposed therebetween; and a merged-type-magnetic head composed of areader using a magneto-resistive effect and a single-pole-type writerfor perpendicular magnetic recording.

Further, a hard disk drive comprises: the above-described magneticrecording medium, an energy generation means for applying a recordingenergy to the magnetic recording medium; an energy focusing means forfocusing the recording energy onto the recording medium; a magneticfield generation means for generating a magnetic field in the vicinityof the focus position of the recording energy; and a reader using amagneto-resistive effect for reproducing a signal recorded on therecording medium. In particular, a light with a wavelength of 350 to1600 nm is used as the means for applying a recording energy to themagnetic recording medium.

The magnetic recording medium in accordance with the present inventionis manufactured by the following method. The method comprises the stepsof: chemically synthesizing alloy nano-particles in such a state as tobe surrounded by a covering of a carbon-containing organic compound, thealloy nano-particles undergoing a transition into an L10 structurethrough an order-disorder transition to exhibit magnetic properties,each of the alloy nano-particles comprising at least one non-magneticelement added thereto, or each of the alloy nano-particles being soconfigured that an L10 alloy core is surrounded by a covering filmcomprising at least one non-magnetic element; applying thenano-particles onto a substrate; heat-treating a nano-particle filmapplied on the substrate so as to cause the nano-particles to undergo anorder-disorder transition and thereby to exhibit magnetic propertieswhile applying a magnetic field in a specific direction to the alloynano-particles; and solidifying (ex., carbonizing) the organic compoundsurrounding the nano-particles at a higher temperature than thetemperature causing the order-disorder transition.

The invention encompasses other embodiments of a method and apparatus,which are configured as set forth above and with other features andalternatives.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings. Tofacilitate this description, like reference numerals designate likestructural elements.

FIG. 1A is a cross-sectional view of an example of a magnetic recordingmedium, in accordance with the present invention;

FIG. 1B is a cross-sectional view of an example of a magnetic recordingmedium, in accordance with the present invention;

FIG. 1C is a cross-sectional view of an example of a magnetic recordingmedium, in accordance with the present invention;

FIG. 2A is part of a schematic diagram for illustrating the principle ofthe lowering in ordering temperature to be used in the presentinvention;

FIG. 2B is part of a schematic diagram for illustrating the principle ofthe lowering in ordering temperature to be used in the presentinvention;

FIG. 2C is part of a schematic diagram for illustrating the principle ofthe lowering in ordering temperature to be used in the presentinvention;

FIG. 2D is part of a schematic diagram for illustrating the principle ofthe lowering in ordering temperature to be used in the presentinvention;

FIG. 3 is a transmission electron microscope photograph of the magneticrecording medium in accordance with the present invention;

FIG. 4A is a schematic diagram for showing one example of a method formanufacturing the magnetic recording medium of the present invention;

FIG. 4B is a schematic diagram for showing one example of a method formanufacturing the magnetic recording medium of the present invention;

FIG. 4C is a schematic diagram for showing one example of a method formanufacturing the magnetic recording medium of the present invention;

FIG. 4D is a schematic diagram for showing one example of a method formanufacturing the magnetic recording medium of the present invention;

FIG. 5 shows a temperature control profile in manufacturing of themagnetic recording medium of the present invention;

FIG. 6 is a schematic diagram for showing a part of a hard disk drivecomposed of an example of the magnetic recording medium of the presentinvention wherein the direction of the axes of easy magnetization is atan angle of roughly 0 degrees with respect to the substrate plane, andan in-plane magnetic recording head;

FIG. 7 is a schematic diagram for showing a part of another example ofthe hard disk drive of FIG. 6, wherein a reader of a CPP structure isused as-the reader in FIG. 6;

FIG. 8 is a schematic diagram for showing a part of a hard disk drivecomposed of an example of the magnetic recording medium of the presentinvention wherein the direction of the axes of easy magnetization is atan angle of roughly 90 degrees with respect to the substrate plane, anda writer for perpendicular magnetic recording;

FIG. 9 is a schematic diagram for showing a part of a hard disk drivecomposed of an example of the magnetic recording medium of the presentinvention wherein the direction of the axes of easy magnetization is atan angle of roughly 45 degrees with respect to the substrate plane, anda writer for perpendicular magnetic recording;

FIG. 10 is a cross-sectional view of a magnetic nano-particle of acore-shell structure;

FIG. 11 is a schematic diagram for showing a part of a hard disk driveequipped with a heat-assisted type writer for perpendicular magneticrecording;

FIG. 12A is part of a schematic diagram of a hard disk drive equippedwith the writer for perpendicular magnetic recording of the presentinvention; and

FIG. 12B is part of a schematic diagram of a hard disk drive equippedwith the writer for perpendicular magnetic recording of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An invention for a magnetic recording medium, hard disk drive using thesame and manufacturing method thereof is disclosed. Numerous specificdetails are set forth in order to provide a thorough understanding ofthe present invention. It will be understood, however, to one skilled inthe art, that the present invention may be practiced without some or allof these specific details.

Prior to the explanation of examples of the present invention, adescription will be given to the principle of the lowering of theordering temperature for use in the present invention.

An L10 type alloy such as FePt alloy takes on an irregularface-centered-cubic structure as shown in FIG. 2A immediately afterbeing fabricated either through deposition in high vacuum by sputteringor the like, or by the method using chemical synthesis as in the presentinvention. The irregular face-centered-cubic structure is characterizedin that atoms of Fe and Pt are arranged at random. In order that thealloy may exhibit magnetic properties, the structure is required to bechanged into the ordered (L10) structure in which atoms of Fe and Ptwhich are elements constituting the alloy core nano-particles areorderly aligned layer by layer as shown in FIG. 2B.

The state of FIG. 2A can be crystallographically referred to as ametastable state. The proper stable state is considered to be the stateof FIG. 2B. However, the alloy core nano-particles invariably take onthe irregular structure as shown in FIG. 2A when manufactured at aroundroom temperature. When the alloy core nao-particles are subjected to aheat treatment, the nao-particles come to the stable state as shown inFIG. 2B due to the diffusion of the Fe and Pt atoms. This is thephenomenon called “order transition”. In general, the orderingtemperature is as high as 550 to 600° C. This is due to the fact thatthe inter-diffusion coefficient of Fe and Pt which are elementsconstituting the alloy core nano-particles is small. The lowering inordering temperature requires an increase in inter-diffusion coefficientof the elements constituting the alloy core nano-particles.

In the present invention, as a first method for lowering the orderingtemperature of the core alloy, there is employed a method in which athird element having a different ion radius is added thereto. If a thirdelement different in ion radius from the elements constituting the corealloy, for example, Fe (0.780 Å for 2+ ion) and Pt(0.80 Å for 2+ ion) issolid-solved in the core alloy, the surrounding portion of the atom ofthe added third element is distorted as shown in FIG. 2C. Each atomaround such a distorted portion is present at a position unstable interms of energy, so that diffusion tends to occur. Diffusion occurs withease based on such a region as a core, and hence the orderingtemperature of the core alloy nano-particles is lowered.

Table 1 shows the difference between the ion radius t2 of the element(Cu, Ag, Sn, or Sb) to be used as the third element and the ion radiust1 of the core element (Fe, Co, Pt, or Pd) constituting the orderedalloy (definition: (t2−t1/t1×100%) TABLE 1 Cu²⁺ Ag⁺ Sn²⁺ Sb³⁺ Fe²⁺ −6.4147.40 19.23 −2.56 Co²⁺ −2.05 54.36 24.83 2.01 Pt²⁺ −8.75 43.75 16.25−5.00 Pd²⁺ −15.1 33.72 8.14 −10.00

If the difference in ion radius is too large, the third element will notbe solid-solved in the ordered alloy of the core. From such a viewpoint,as the third element to be added, a material such as. Cu or Sb issuperior to a noble metal such as Ag. More preferably, a material ofwhich the value of the difference in ion radius from the elementconstituting the core alloy is single digit is desirably used.

As a second method for lowering the ordering temperature of the corealloy, there is employed a method in which the nano-particles of thecore alloy are surrounded using an element having a different latticeconstant as a shell. As the shell for surrounding the nano-particles,there is used a metal having a different lattice constant from thelattice constant of the ordered alloy constituting the nano-particles.By doing so, the position of the atoms present at the interface with thecore alloy is expanded (or shrunk) by being pulled by the surroundingmetal lattice as shown in FIG. 2D.

The atoms in the vicinity of the interface with the core alloy diffusewith ease, and hence ordering occurs at a lower temperature from theinterface as a starting point. Herein, the lattice constants d1 of noblemetal elements are as follows: Pd: 3.89 Å (cubic lattice), Ag: 4.09 Å(cubic lattice), Pt: 3.92 Å (cubic lattice), and Au: 4.08 Å (cubiclattice). The lattice constant d2 of the core alloy in unordered form is3.90 Å for FePt. Thus, the differences in lattice constant when noblemetals are used as the shells are shown in Table 2. TABLE 2 Differencein lattice constant (definition: (d1 − d2)/d2 × 100%, the value of axisa is used for the ordered alloy) Pd Ag Pt Au FePt 0.26 4.87 0.51 4.61

When the difference in lattice constant is too large, it is conceivablethat the atoms of the shell layer and the atoms of the core layer at theinterface will not be epitaxially bonded to each other closely as shownin FIG. 2D. On the other hand, when the difference in lattice constantis too small, it is conceivable that less effects are produced. When thedifference in lattice constant from the core alloy is not more than 5%,substantial effects of lowering the ordering temperature cannot beexpected. Therefore, as a noble metal to be used as the shell forsurrounding the core alloy, as shown in Table 3, an element of which thedifference in lattice constant from the core alloy is not less than 5%and not more than 30% is more preferred. TABLE 3 Differences in latticeconstant from preferred element group other than Ag Cu Sn Pb Sb Bi FePt−7.18 −18.46 26.9 10.51 16.7

Below, the present invention will be described by way of examples withreference to the accompanying drawings. Each of FIGS. 1A to 1C shows oneexample of a magnetic recording medium in accordance with the presentinvention. FIG. 1A shows an example in which the present invention hasbeen applied to a so-called in-plane recording medium wherein the angleformed between the axis of easy magnetization and the substrate plane isroughly zero degrees. FIG. 1B shows an example of a magnetic recordingmedium wherein the angle formed between the axis of easy magnetizationand the substrate plane is roughly 45 degrees. FIG. 1C shows an exampleof a so-called perpendicular magnetic recording medium wherein the angleformed between the axis of easy magnetization and the substrate plane is90 degrees.

In FIGS. 1A to 1C, a reference numeral 101 denotes a substrate (ex.,glass or Al substrate); 102, an underlayer; 103, magneticnano-particles; 104, a covering surrounding the magnetic nano-particles;105, a surface protective film; 106, a soft magnetic underlayer (ex.,FeTaC or CoZrNb); 107, an underlayer for the soft magnetic underlayer;and 108, an interlayer for cutting the magnetic interaction between thesoft magnetic underlayer 106 and the magnetic nano-particles 103.

FIG. 3 is a diagram showing one example of a photograph of the magneticrecording medium of the present invention observed under a transmissionelectron microscope. Black points are magnetic nano-particles with anaverage nano-particle diameter of 5.5 nm. The bright area between theblack points is a covering of carbon which is an organic compound. It isherein shown that the nano-particles are regularly separated from oneanother at a substantially uniform spacing by the covering of carbon.Further, in the example of FIG. 3, the nano-particle diameter dispersionof the magnetic nano-particles is 7%. The nano-particle diameterdispersion is desirably not more than 10%, and in particular, morepreferably not more than 7%. With the magnetic recording medium of thisexample, the nano-particle diameter dispersion falls within the morepreferred range.

The magnetic nano-particle to be used in the present invention is, firstof all, composed of an alloy material prepared by adding any of Cu, Sn,Pb, Sb, and Bi to an alloy made of any of Fe and Co and any of Pt andPd. Alternatively, it takes on a structure in which the alloy of any ofFe and Co and any of Pt and Pd serves as a core and Cu, Sn, Pb, Sb, orBi (shell) surrounds therearound. Below, the reason why the alloynano-particles of the material or the structure are preferred formanufacturing the magnetic recording media as shown in FIGS. 1A to 1Cwill be explained while describing a manufacturing method thereof.

FIGS. 4A to 4D show one example of a manufacturing method of themagnetic recording medium of the present invention. First, as shown inFIG. 4A, alloy nano-particles with a diameter of 3 to 10 nm arechemically synthesized. The chemically synthesized nano-particles 301are each surrounded by a carbon-containing organic compound 302 to forma colloid in an appropriate solvent 303. The alloy colloid particles aredeposited in a monolayer on the underlayer 102 for FIG. 1A, or on theinterlayer 108 for FIGS. 1B and 1C. The deposition can be accomplishedby several methods including, for example, general methods in which anorganic material is coated and deposited on a substrate, such as dipcoating and spin coating, and a Langmuir-Blodgett method.

FIG. 4B shows the step. FIG. 4B shows one example for the case where themagnetic recording medium of FIG. 1B or 1C is manufactured. As is wellknown, the alloy particles of any of Fe and Co and any of Pt and Pdimmediately after synthesis are in an irregular face-centered cubic(fcc) structure. The alloy particles do not exhibit magnetic propertiesin this state. In order that the alloy particles may exhibit magneticproperties, the following process must be performed. As shown in FIG.4C, the alloy particles are heat-treated to induce an order-disordertransition, so that the crystal structure of the alloy particlesundergoes a transition to an ordered L10 structure.

However, the temperature at which the transition occurs is generally asvery high as 550 to 600° C. If such a high temperature heat treatment isperformed, first, the nano-particles which have been aligned in amonolayer so carefully agglomerate together, and grow into a largeagglomerate nano-particles. This increases the nano-particle diameter,which is unfavorable for implementing a high-density magnetic recordingmedium. Secondly, when the high temperature heat treatment is performed,the organic compound surrounding the alloy nano-particles 301 aresolidified.

Originally, the crystalline axes of the alloy nano-particles depositedon the substrate are oriented at random. Therefore, the magneticnano-particles magnetized after the heat treatment were also fixed bythe organic compound surrounding the magnetic nano-particles with theaxes of easy magnetization oriented at random. With a magnetic recordingmedium to be made available for actual use, it is essential that thedirections of axes of easy magnetization are aligned in the samedirection as much as possible. For this reason, such magneticnano-particle film cannot be used as a magnetic recording medium.

Thirdly, in particular, when the magnetic nano-particle film is formedon the soft magnetic underlayer 106 as shown in FIGS. 1B and 1C, a hightemperature heat treatment at 550 to 600° C. adversely affects themagnetic characteristics of the soft magnetic underlayer. Accordingly,it is not possible to keep desirable characteristics. In the presentinvention, for synthesis, to an alloy composed of any of Fe and Co andany of Pt and Pd, a third element, specifically, Cu, Sn, Pb, Sb, Bi, orthe like is added. Thus, the synthesis is accomplished. These atomsenter into the lattice positions occupied by Fe or Co and Pt or Pd togenerate a stress in the crystal.

In general, the order-disorder transition is triggered by the stress inthe crystal. Accordingly, for the alloy to which the appropriate thirdatoms have been added as in this example, the temperature causing theorder-disorder transition is lowered largely. The relationship betweenthe amount of the third element added and the temperature causing theorder-disorder transition varies depending upon the kinds of the basealloy and the atoms to be added. In general, an amount of the atomsadded in a range of 5 to 20% lowers the order-disorder transitiontemperature to not more than 300° C. In particular, when Cu is added inan amount of about 10% to a preferred composition, for example, FePtnano-particles, it is possible to largely lower the temperature to 250°C.

Alternatively, another method for lowering the ordering temperature ofthe alloy nano-particles is as follows. For synthesis, the alloycomposed of any of Fe and Co and any of Pt and Pd is first synthesized.Then, the shell portion composed of Cu, Sn, Pb, Sb, Bi, or the like isfabricated so as to surround the core of the alloy. By doing so, a largestress acts on the interface of the alloy core with the shell. As aresult, it is possible to set the order-disorder transition temperatureat generally not more than 300° C.

If the alloy nano-particles of which the order-disorder transitiontemperature has been thus lowered to not more than 300° C. are used, itis possible to align the axes of easy magnetization of the magneticnano-particles in one direction by performing a heat treatment in amagnetic field as shown in FIG. 4C. Then, as shown in FIG. 4D, the heattreatment temperature is raised up to the solidification temperature ofthe organic compound (ex., carbon) surrounding the magneticnano-particles 301 to sufficiently solidify the organic compound. Thus,the magnetic nano-particles are fixed to the substrate with the axes ofeasy magnetization of the magnetic nano-particles held in a prescribeddirection.

FIG. 5 shows the changes in temperature when the foregoing heattreatment in a magnetic field is performed. The alloy nano-particlesdeposited in a monolayer on the substrate as shown in FIG. 4C are heatedunder a magnetic field, up to the temperature at which theorder-disorder transition is initiated, for example, 250° C. At thisheat treatment temperature, the organic compound surrounding the alloynano-particles has not yet been solidified completely. Therefore, thealloy nano-particles change into an L10 structure through theorder-disorder transition, so that the directions of magnetization ofthe alloy nano-particles magnetized in random directions rotate in thedirection of applied magnetic field to be uniformly aligned.

By setting the direction of magnetic field to be applied at this step ata given angle with the substrate plane, it is possible to set thedirection of axis of easy magnetization along the direction at adesirable angle with respect to the substrate plane. For example, if thedirection of magnetic field to be applied is set parallel to thesubstrate plane, it is possible to form the in-plane magnetic recordingmedium as shown in FIG. 1A. If the direction of magnetic field is set tobe the direction at an angle of 45 degrees with respect to the substrateplane, it is possible to form the magnetic recording medium as shown inFIG. 1B. If the direction of magnetic field is set to be the directionat an angle of 90 degrees with respect to the substrate plane, it ispossible to form the perpendicular magnetic recording medium as shown inFIG. 1C. Subsequently, the heat treatment temperature is raised up tomore than 300° C., for example, up to 350° C., so that thecarbon-containing organic compound around the nano-particles issufficiently solidified. The respective magnetic alloy nano-particlesare firmly fixed in the process of solidification. Finally, the magneticfield is cut, and the temperature is decreased to room temperature.Thus, a protective film 105 for anti-sliding purpose is formed on thesurface, completing the medium manufacturing process.

FIG. 6 is a diagram for showing a schematic configuration of a hard diskdrive using a magnetic recording medium composed of a substrate 101, anunderlayer 102, magnetic nano-particles 103 of which the-axes of easymagnetization form an angle of roughly zero degrees with respect to thesubstrate plane, a covering 104 surrounding the magnetic nano-particles,and a surface protective film 105, and a merged-type-magnetic headhaving a reader using a magneto-resistive effect for reproduction, and awriter in a ring form for recording.

Herein, a reference numeral 502 denotes a substrate constituting thebase portion of a magnetic slider; 503, a lower shield; 504 aninsulating film; 505, a magnetic sensor applying a magneto-resistiveeffect showing an anisotropic magneto-resistive effect (AMR) or agiant-magneto-resistive effect (GMR); 506, an upper shield; 507, aspacer layer; 508, a lower magnetic pole; 509, an upper magnetic pole;510, a coil for inducing a magnetic field between the magnetic poles;and 501, a protective film. The magnetic sensor film indicated by 505 isnot shown in detail. When the GMR is used, the magnetic sensor film iscomposed of a multilayered film of, for example,underlayer/anti-ferromagnetic layer/pinned layer/metal layer/freelayer/cap layer. Further, permanent magnets for inhibiting theinstability in magnetization of the free layer are disposed at oppositeends of the sensor film along the direction perpendicular to the paperplane.

FIG. 7 shows an example of the hard disk drive of FIG. 6 in which areader of a CCP (current perpendicular to plane) system for passing adetection current perpendicularly to the sensor film surface is used asthe reader using a magneto-resistive effect. A reference numeral 601denotes a lower electrode layer; 602, a magnetic sensor film applying amagneto-resistive effect; and 603, an upper electrode layer. A currentpasses between the upper shield 506 and the lower shield 503. When theGMR is used, as with FIG. 6, the magnetic sensor film is composed of amultilayered film of, for example, underlayer/anti-ferromagneticlayer/pinned layer/metal layer/free layer/cap layer. When a tunnelmagneto-resistive effect (TMR) is used, the magnetic sensor film iscomposed of a multilayered film of, for example,underlayer/anti-ferromagnetic layer/pinned layer/insulating layer/freelayer/cap layer. Further, as with FIG. 6, permanent magnets forinhibiting the instability in magnetization of the free layer aredisposed at opposite ends of the sensor film along the directionperpendicular to the paper plane.

FIG. 8 is a diagram for showing a schematic configuration of a hard diskdrive using a magnetic recording medium composed of a substrate 101, anunderlayer 108, a soft magnetic underlayer 106, an interlayer 107,magnetic nano-particles 103 of which the axes of easy magnetization forman angle of roughly 90 degrees with respect to the substrate plane, acovering 104 surrounding the magnetic nano-particles, and a surfaceprotective film 105, a merged-type-magnetic head having a reader using amagneto-resistive effect for reproduction, and a single-pole-type writerfor perpendicular magnetic recording. Herein, the reference numerals 501to 507 respectively denote the same elements as in FIG. 6. Further, evenif a reader using the magneto-resistive effect of the CPP type obtainedby changing the elements 504 and 505 into the elements 601 to 603 ofFIG. 7 is used, the same effects are produced. Further, referencenumerals 701 and 702 denote a main magnetic pole and a sub magnetic poleof a single-pole-type writer, respectively.

FIG. 9 shows an example of the hard disk drive of FIG. 8, using amagnetic recording medium in which the axes of easy magnetization of themagnetic nano-particles 103 form an angle of roughly 45 degrees withrespect to the substrate plane.

The magnetic recording performances of the magnetic recording medium ofthe present invention will be described taking the magnetic recordingmedium used in FIG. 8 as an example. For the magnetic recording mediumused in FIG. 8, as indicated from the TEM photograph of FIG. 3, theaverage diameter of nano-particles was 6.5 nm and the spacing betweenthe nano-particles was about 2 nm. The alloy nano-particles used are thenano-particles with a composition of (FePt)₈₉Cu₁₁. The coercive force Hcin the direction perpendicular to the film surface of the nano-particlefilm determined by a VSM was 875 kA/m (11 kOe) and the magneticanisotropy energy Ku determined by a torque magnetometer was 1.46×10⁶J/m². The KuV/kT at this stage is estimated to be about 54, which is thevalue enough for ensuring the thermal stability. Thus, it was possibleto obtain the characteristics unobtainable with a conventional magneticnano-particle medium in which the axes of easy magnetization areoriented three dimensionally at random.

Further, a recording experiment was carried out by using asingle-pole-type head expected to be capable of generating a maximummagnetic field of 1.2 MA/m (15 kOE) by micro-magnetic calculations usinga three-dimensional finite element method. As a result, an overwriteperformance of more than 35 dB at a magnetomotive force of 0.3 AT(recording of a signal of 400 kFCl on a signal of 60 kFCl) was shown.This indicated that the hard disk drive composed of a combination of themagnetic recording medium having an alloy nano-particle layer and asingle-pole-type writer in accordance with the present invention has asufficient recording performance.

The alloy nano-particles used for the magnetic recording medium of FIG.8 are the nano-particles of the type in which a third element has beenadded. In the nano-particles of this type, the third element isincorporated in the alloy structure itself. Therefore, the magneticproperties such as the magnetic anisotropy energy and the coercive forceto be exhibited are smaller in value than the magnetic propertiesexhibited by pure L10 type alloys. In order to increase the magneticanisotropy energy Ku and lower the disorder-order transition temperatureof the L10 alloy for further enhancing the thermal stability, thefollowing procedure is effective. As shown in FIG. 10, nano-particles ofa so-called core-shell structure, in each of which for example, a metal902 such as Cu surrounds around, for example, a FePt core particle 901,are chemically synthesized. The resulting nano-particles are depositedon the substrate for use as a magnetic recording medium.

The average diameter of the alloy nano-particles obtained as a result ofthe chemical synthesis was 6.5 nm. A high resolution TEM observationindicates that the nano-particle diameter of the FePt portion of thecore was 5.5 nm. The coercive force Hc in the direction perpendicular tothe film surface of the nano-particle film determined by a VSM was 1590kA/m (20 kOe) and the magnetic anisotropy energy determined by a torquemagnetometer was 3×10⁶ J/m². In this step, the KuV/kT was 63, indicatingthat the film is thermally more stable than the above-described example.

However, in order to perform magnetic recording on the magneticrecording medium having such a high magnetic anisotropy energy, amagnetic field strength as high as not less than 2385 kA/m (30 kOe) isrequired. Thus, it is impossible to generate such a large magnetic fieldstrength with a writer using a material having a saturation magneticflux density of not more than 2.4 T. Under such circumstances, in thisexample, the following method is adopted. For example, as shown in FIG.11, an optical waveguide 1001 for guiding a light is disposed inproximity to the main magnetic pole 701 of the single-pole-type writerfor recording. Thus, the nano-particle layer is heated by a light 1002emitted from the optical waveguide 1001. As a result, the coercive forceHc of the L10 alloy is reduced to perform recording. The wavelength ofthe light to be used is desirably a wavelength such that the light willbe absorbed in the nano-particle layer, for example, 350 to 1600 nm.However, visible light, particularly, violet light wavelengths arepreferred for reducing the size of the optical waveguide and reducingthe emitted light size.

The temperature dependence of the coercive force Hc of the nano-particlelayer was measured. As a result, it was observed that the coercive forceHc of the nano-particle layer was reduced roughly linearly with anincrease in temperature, and that it was 875 kA/m (11 kOe) at atemperature of 200° C. Then, the optical power to be inputted to theoptical waveguide was controlled so that the temperature of thenano-particle layer becomes 200° C. Thus, a recording experiment wascarried out. As a result, when a single-pole-type head expected to becapable of generating a maximum magnetic field of 1.2 MA/m (15 kOe) wasused, an overwrite performance of more than 35 dB at a magnetomotiveforce of 0.3 AT (recording of a signal of 400 kFCl on a signal of 60kFCl) was observed. This indicated that the hard disk drive composed ofa combination of the magnetic recording medium having a nano-particlelayer and the single-pole-type writer in accordance with the presentinvention has a sufficient recording performance.

FIGS. 12A and 12B show a schematic diagram of a hard disk drive usingthe magnetic recording medium of the present invention (however, theenlargement factor of the diagram is not uniform). FIG. 12A is a planview, and FIG. 12B is a cross-sectional view. The hard disk driveperforms recording and reproduction of a magnetized signal on a disk1102 in which the magnetic recording medium is formed by a magnetic head1103 attached on a slider fixed at the tip of a suspension arm 1105. Theprocessing of the signal reproduced by the magnetic head 1103 isperformed by a circuit 1101. Further, the movement of the head to aprescribed information recorded position is performed by a rotaryactuator 1104.

Other Embodiments

The present invention includes, but is not limited to, the followingadditional embodiments.

A hard disk drive is provided that comprises a magnetic recording mediumincluding, a substrate, and a magnetic recording layer formed on thesubstrate, the magnetic recording layer having an organic compound andalloy nano-particles surrounded by the organic compound, wherein thealloy nano-particles aligned substantially uniformly along a directionat an angle of roughly 0 degrees with respect to the substrate to formaxes of easy magnetization, and wherein the alloy nano particles areconfigured to undergo a transition into an L10 structure at an orderingtemperature lower than a stiffness, or cure, temperature of the organiccompound to exhibit magnetic properties, and wherein the organiccompound is solidified with the axes of easy magnetization; and amerged-type-magnetic head including a reader configured to use amagneto-resistive effect and to use a writer in a ring form.

A hard disk drive is provided that comprises a magnetic recordingmedium, comprising: a substrate; a soft magnetic underlayer on thesubstrate; and a magnetic recording layer formed on the substrate withthe soft magnetic layer interposed therebetween, the magnetic recordinglayer comprising an organic compound and alloy nano-particles surroundedby the organic compound and arranged at a substantially uniform spacing,the alloy nano-particles undergoing a transition into an L10 structureat an ordering temperature lower than a stiffness, or cure, temperatureof the organic compound to exhibit magnetic properties, wherein theorganic compound has been solidified with the axes of easy magnetizationof the alloy nano-particles aligned substantially uniformly along adirection at an angle of roughly 45 degrees or roughly 90 degrees withrespect to the substrate plane; and a merged-type-magnetic headcomprising a reader using a magneto-resistive effect and asingle-pole-type writer for perpendicular magnetic recording.

This hard disk drive may have a light with a wavelength of 350 to 1600nm used as the energy generation means.

A hard disk drive is provided that comprises a magnetic recordingmedium, comprising: a substrate; and a magnetic recording layer formedon the substrate, the magnetic recording layer comprising an organiccompound and alloy nano-particles surrounded by the organic compound andarranged at a substantially uniform spacing, the alloy nano-particlesundergoing a transition into an L10 structure at an ordering temperaturelower than a stiffness temperature of the organic compound to exhibitmagnetic properties, wherein the organic compound has been solidifiedwith the axes of easy magnetization of the alloy nano-particles alignedsubstantially uniformly along a specific direction with respect to thesubstrate plane; an energy generation means for applying a recordingenergy to the magnetic recording medium; an energy focusing means forfocusing the recording energy onto the recording medium; a magneticfield generation means for generating a magnetic field in the vicinityof the focus position of the recording energy; and a reader using amagneto-resistive effect for reproducing a signal recorded on therecording medium.

A method for manufacturing a magnetic recording medium is provided thatcomprises chemically synthesizing alloy nano-particles surrounded by anorganic compound so as to be aligned substantially uniformly along aspecific direction with respect to a substrate to form axes of easymagnetization; placing the alloy nano-particles on the substrate;applying heat energy to the alloy nano-particles such that the alloynano-particles are configured to undergo an order-disorder transitioninto an L10 structure at an ordering temperature lower than a stiffnesstemperature of the organic compound to exhibit magnetic properties;solidifying the organic compound at a higher temperature than theordering temperature while applying a magnetic field in a specificdirection to the alloy nano-particles having the magnetic properties;and forming a magnetic recording layer on the substrate in such a statethat the organic compound is solidified with the axes of easymagnetization.

This method may be such that the chemically synthesizing step includesat least one of a step of adding at least one non-magnetic element tothe alloy nano-particles and a step of forming a covered layercomprising at least one non-magnetic element as the surrounding surfaceof each of the alloy nano-particles.

This method may be such that each of the alloy nano-particles comprisesan alloy of any of Fe and Co and any of Pt and Pd as a base, and thenon-magnetic element to be added thereto is any of Cu, Sn, Pb, Sb, andBi.

This method may be such that each of the alloy nano-particles comprisesan alloy of any of Fe and Co and any of Pt and Pd as a core, and theelement constituting the layer covering therearound is any of Cu, Sn,Pb, Sb, Bi, and Ag.

A method for manufacturing a magnetic recording medium is provided thatcomprises preparing alloy nano-particles comprising an alloy which willundergo a transition to an L10 structure through an order-disordertransition to exhibit magnetic properties, and at least one non-magneticelement added thereto, or a covering film comprising at least onenon-magnetic element covering therearound, and chemically synthesizingthe alloy nano-particles so as to be arranged at a substantially uniformspacing and surrounded by an organic compound; applying the alloynano-particles onto a substrate; heat-treating a nano-particle filmapplied on the substrate at an ordering temperature lower than astiffness temperature of the organic compound so as to effect anorder-disorder transition of the nano-particles while applying amagnetic field in a specific direction to the alloy nano-particles; andsolidifying the organic compound at a higher temperature than theordering temperature while applying a magnetic field in a specificdirection to the alloy nano-particles, wherein a magnetic recordinglayer is formed on the substrate in such a state that the organiccompound has been solidified with the axes of easy magnetization of thealloy nano-particles aligned substantially uniformly along a specificdirection with respect to the substrate.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

1. A method for manufacturing a magnetic recording medium comprising:chemically synthesizing alloy nano-particles surrounded by an organiccompound so as to be aligned substantially uniformly along a firstdirection with respect to a substrate to form axes of easymagnetization; placing the alloy nano-particles on the substrate;applying heat energy to the alloy nano-particles such that the alloynano-particles are configured to undergo an order-disorder transitioninto an L10 structure at an order-disorder transition temperature lowerthan a solidification temperature of the organic compound to exhibitmagnetic properties; solidifying the organic compound at a highertemperature than the order-disorder transition temperature whileapplying a magnetic field in a second direction to the alloynano-particles having the magnetic properties; and forming a magneticrecording layer on the substrate in such a state that the organiccompound is solidified with the axes of easy magnetization.
 2. Thismethod according to claim 1, wherein the chemically synthesizing stepincludes at least a step of adding at least one non-magnetic element tothe alloy nano-particles and a step of forming a covered layer includingat least one non-magnetic element as a surrounding surface of each ofthe alloy nano-particles.
 3. This method according to claim 1, whereineach of the alloy nano-particles includes a base alloy of one of Fe andPt, Fe and Pd, Co and Pt, Co and Pd, and the non-magnetic element to beadded thereto is one of Cu, Sn, Pb, Sb, and Bi.
 4. This method accordingto claim 1, wherein each of the alloy nano-particles includes a basealloy core of one of Fe and Pt, Fe and Pd, Co and Pt, Co and Pd, and theelement constituting the layer covering therearound is one of Cu, Sn,Pb, Sb, Bi, and Ag.
 5. A method for manufacturing a magnetic recordingmedium comprising: preparing alloy nano-particles including an alloywhich will undergo a transition to an L10 structure through anorder-disorder transition to exhibit magnetic properties, and at leastone non-magnetic element added thereto, or a covering film including atleast one non-magnetic chemically synthesizing the alloy nano-particlesso as to be arranged at a substantially uniform spacing and surroundedby an organic compound; applying the alloy nano-particles onto asubstrate; heat-treating a nano-particle film applied on the substrateat an order-disorder transition temperature lower than a solidificationtemperature of the organic compound so as to effect an order-disordertransition of the nano-particles while applying a magnetic field in afirst direction to the alloy nano-particles; and solidifying the organiccompound at a higher temperature than the order-disorder transitiontemperature while applying a magnetic field in a second direction to thealloy nano-particles, wherein a magnetic recording layer is formed onthe substrate such that the organic compound has been solidified withthe axes of easy magnetization of the alloy nano-particles alignedsubstantially uniformly along a third direction with respect to thesubstrate.